Field
Embodiments disclosed herein generally relate to fixed cutter cutting tools having improved formation evacuation elements.
Background Art
In drilling a borehole in the earth, such as for the recovery of hydrocarbons or for other applications, it is conventional practice to connect a drill bit on the lower end of an assembly of drill pipe sections that are connected end-to-end so as to form a “drill string.” The bit is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating bit engages the earthen formation causing the bit to cut through the formation material by either abrasion, fracturing, or shearing action, or through a combination of all cutting methods, thereby forming a borehole along a predetermined path toward a target zone.
Many different types of drill bits have been developed and found useful in drilling such boreholes. Two predominate types of drill bits are roller cone bits and fixed cutter (or rotary drag) bits. Most fixed cutter bit designs include a plurality of blades angularly spaced about the bit face. The blades project radially outward from the bit body and form flow channels, or junk slots, therebetween. In addition, cutting elements are typically grouped and mounted on several blades in radially extending rows. The configuration or layout of the cutting elements on the blades may vary widely, depending on a number of factors such as the formation to be drilled.
A conventional drag bit is shown in FIG. 1. The drill bit 10 includes a bit body 12 and a plurality of blades 14 extending radially from the bit body 12. The blades 14 are separated by channels or junk slots 16 that enable drilling fluid to flow between and both clean and cool the blades 14 and cutters 18. Cutters 18 are held in the blades 14 at predetermined angular orientations and radial locations to present working surfaces 20 with a desired back rake angle against a formation to be drilled. Typically, the working surfaces 20 are generally perpendicular to the axis 19 and side surface 21 of a cylindrical cutter 18. Thus, the working surface 20 and the side surface 21 meet or intersect to form a circumferential cutting edge 22.
Orifices are typically formed in the drill bit body 12 and positioned in the junk slots 16. The orifices are commonly adapted to accept nozzles 23, wherein the orifices may also be referred to as nozzle bores. The orifices allow drilling fluid to be discharged through the bit in selected directions and at selected rates of flow between the cutting blades 14 for lubricating and cooling the drill bit 10, the blades 14 and the cutters 18. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the geological formation. Without proper flow characteristics, insufficient cooling of the cutters may result in cutter failure during drilling operates. The junk slots 16, which may also be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (not shown).
The drill bit 10 includes a shank 24 and a crown 26. The shank 24 is typically formed of steel or a matrix material and includes a threaded pin 28 for attachment to a drill string. The crown 26 has a cutting face 30 and outer side surface 32. The particular materials used to form drill bit bodies are selected to provide adequate strength and toughness, while providing good resistance to abrasive and erosive wear.
The combined plurality of surfaces 20 of the cutters 18 effectively forms the cutting face 30 of the drill bit 10. Once the crown 26 is formed, the cutters 18 are positioned in the cutter pockets 34 and affixed by any suitable method, such as brazing, adhesive, mechanical means such as interference fit, or the like. The design depicted provides the cutter pockets 34 inclined with respect to the surface of the crown 26. The cutter pockets 34 are inclined such that cutters 18 are oriented with the working face 20 at a desired rake angle in the direction of rotation of the bit 10 so as to enhance cutting. It will be understood that in an alternative construction (not shown), the cutters can each be substantially perpendicular to the surface of the crown, while an ultra-hard surface is affixed to a substrate at an angle on a cutter body or a stud so that a desired rake angle is achieved at the working surface.
During drilling operations, a drag bit may shear the formation being drilled, thereby generating formation cuttings. Such cuttings often become trapped and accumulate within select regions of the drill bit, such as within the bit junk slots. Accumulated cuttings may interfere with fluid flow through the bit junk slots and eventually lead to bit balling. When drilling operations are conducted in formations containing shale, accumulated cuttings may be referred to as shale-packing. There have been various attempts at reducing accumulation of cuttings, such as designing particular placement of fluid nozzles or drag bit blade shapes. However, a need still exists for reduced cuttings accumulation and shale packing.